1. Field of the Invention
The present invention relates to a device and a method for detecting a period of an input signal, and more particularly, to a device and a method for detecting a period of an input signal exclusively through a reference clock with (n) times greater accuracy. The present application is based on Korean Patent Application No. 2000-49936, filed Aug. 26, 2000, which is incorporated herein by reference.
2. Related Art
Sampling theory postulates that a signal that varies continuously with time is completely determined by its values at an infinite sequence of equally spaced times if the frequency of these sampling times is greater than twice the highest frequency component of the signal. According to the sampling theory, a period detector used in a CD (Compact Disk) or a DVD (Digital Video Disk) detects a period of an input signal by counting series of sectors to which the signal is input, by two times a reference clock. To perform the above mentioned detecting, rather simple devices such as a counter using two times clock and a comparator identifying symbols of the input signal have been used.
Referring to FIG. 1 illustrating a conventional method for detecting a period of an input signal a, each period of clock b, i.e., two times a reference clock c is counted d and accumulated e at a point which (+) and (−) symbols of the input signal a are changed. The accumulated value “9” prior to a zero cross point is output as a count value e, then the previous count value is initialized to count a new number of clock periods until a next zero cross point. Then, a new count value after a change of the input signal symbols is accumulated until the next change of the symbol, and output as a count value “5”. And the previous count value is initialized repeatedly to count a new number of clock periods. Here, the output count values e of “9” and “5” are divided by n times, where n=2 , thereby a frequency f with resulting values of “4.5” and “2.5” accordingly is detected.
The conventional method for detecting a period of an input signal, as described above, is widely used due to a high restoring rate of original information, and its simple hardware structure. Detecting a period of an input signal with a higher resolution can be done by using n times clock of a reference clock.
A hardware structure for using n times clock is simple when a data transmitting speed of CD/DVD is low. However, a competition over the data transmitting speed is keen at the present time, thus, the hardware structure for using n times clock becomes complex. It is difficult for the present technology to cope with the complex hardware structure for using n times clock of the reference clock to obtain a higher resolution.